Transparent dye-sensitized solar cell and a method for manufacturing the solar cell

ABSTRACT

The present invention relates to a dye-sensitized solar cell (DSC) comprising a porous isolating substrate (30) having a first surface and a second surface, a first porous layer (14) comprising conducting particles printed on the first surface of the porous isolating substrate to form a conductive porous layer, a second porous layer (16) comprising conducting particles printed on the second surface of the porous isolating substrate to form a conductive porous layer, whereby the porous isolating substrate is disposed between the first and second porous layers, a third porous layer (18) comprising light absorbing dye molecules deposited on the first porous layer, and a charge transfer medium for transferring charges between the third and first porous layers. Each of the porous layers comprise a printed pattern including at least one non-transparent portion (24, 25, 26) and at least one transparent portion (20, 21, 22) and the porous isolating substrate comprises at least one transparent portion (32), whereby said transparent portions of the porous layers and said transparent portion of the porous isolating substrate are positioned relative to each other so they form at least one continuous transparent pathway through the solar cell.

FIELD OF THE INVENTION

The present invention relates to a transparent dye-sensitized solarcell. The present invention also relates to a method for manufacturingtransparent dye-sensitized solar cells.

PRIOR ART

Dye-sensitized solar cells (DSC) have been under development over thelast 20 years and work on similar principles as photosynthesis. Unlikesilicon solar cells, these cells obtain energy from sunlight using dyes,which can be manufactured at low cost, environmentally unobtrusive andin abundance.

A conventional sandwich type dye-sensitized solar cell has a few μmthick porous TiO₂ electrode layer deposited onto a transparentconducting substrate. The TiO₂ electrode comprises interconnected TiO₂metal oxide particles with dye molecules adsorbed on the surface of theTiO₂ particles and forms a working electrode. A transparent conductingsubstrate is a transparent conducting oxide deposited onto a glasssubstrate. The transparent conducting oxide layer serves as an electroncollector extracting photo-generated electrons from the workingelectrode. The TiO₂ electrode is in contact with an electrolyte andanother transparent conducting substrate, i.e. a counter electrode.

Sunlight is harvested by the dye, producing photo-excited electrons thatare injected into the conduction band of the TiO₂ particles and furthercollected by the conducting substrate. At the same time, I⁻ ions in theredox electrolyte reduce the oxidized dye and transport the generatedelectron acceptors species to the counter electrode.

Normally, solar cells have a front contact, whereby the currentcollector is positioned on top of the light absorbing layer. The lighthas to pass through the front contact before it can hit the lightabsorbing layer. Consequently, the current collector needs to be bothsufficiently transparent to the incoming light and have sufficientlyhigh electronic conductivity to allow both the passage of maximum amountof light and conduct away the photogenerated electrical current withoutsignificant electrical resistive losses. Unfortunately, materials withhigh transparency have low conductivity and materials with highconductivity have low transparency. The transparent conductors used infront contact solar cells absorb part of the incoming light before ithits the light absorbing layer.

An advantage of DSC solar cell technology is that the current collectorcan be put on the back side of the light absorbing layer using theso-called “back contact” approach. A back contact allows for usage ofextremely high conductivity current collectors that are not transparentto light, i.e. conductor that block light by reflecting light orabsorbing light. The conductivity of the back contact current collectorcan be several orders of magnitude higher compared to the transparentcurrent collectors used in the front contact. The light to electricenergy conversion efficiency of the back contact DSC cell can beincreased significantly, because of the reduced electrical losses, i.e.smaller resistance in the current collector, increased active area andhigher photon flux hitting the light absorbing layer.

FIG. 1 shows an example of a dye-sensitized solar cell comprising aworking electrode 1 including a porous metal oxide with light absorbingmaterial deposited on a top side, a first conductive layer 2 forextracting photo-generated electrons from the working electrode, aporous isolating substrate 4 and a counter electrode including a secondconductive layer 3 arranged on the opposite side of the porous isolatingsubstrate. The first conductive layer 2 is a porous conductive layerdeposited on one side of the porous isolating substrate 4. The secondconductive layer 3 is a porous conductive layer deposited on the otherside of the porous isolating substrate 4. The first and secondconductive layers are printed on the porous isolating substrate. Bothconductive layers 2, 3 consist of particles that are large enough not topenetrate the pores of the porous substrate. The substrate separates theconductive layers physically and electrically in order to avoid directelectronic short circuit between the conductive layers. Further, toallow the first and second conductive layers to be printed on the poroussubstrate, the porous substrate should be suitable for printing.

Pluralities of cells form together a solar cell module. The conductivelayers may be sealed at the edges in order to protect the DSC modulesagainst the surrounding atmosphere, and to prevent the evaporation orleakage of the DSC components inside the cell.

The electrode structure in FIG. 1 is infiltrated with an electricalcharge transfer medium, such as an electrolyte, in the pores of thelight absorbing layer and the porous electrodes and in the pores of theporous substrate. The charge transfer medium forms a continuous layerinside the conductors and between the conductors thereby enablingtransport of electrical charge between the counter electrode and theworking electrode. The first conductive layer is used to collectelectrons generated by the light absorbing layer and to transport theelectrons via an extern electrical circuit (not shown in FIG. 1) to thecounter electrode. The counter electrode is used to transfer theelectrons to the charge transfer medium. The charge transfer mediumtransfers electrons back to the light absorbing layer thereby completingthe electrical circuit. Depending on the nature of the charge transfermedium, either ions or electrons and holes can be transported betweenthe counter electrode and the light absorbing layer.

The charge transfer medium exhibits a certain electrical resistance totransport of charges. The electrical resistance increases with thecharge transport distance. Therefore, when electrical charge istransported between the counter electrode and the light absorbing layerthere will always be a certain electrical resistive loss in the chargetransfer medium. By minimizing the distance between the counterelectrode and the light absorbing layer it is possible to minimize theresistive loss. By making the porous substrate thinner the resistivelosses can be reduced. However, when the porous substrate becomesthinner, it also becomes more mechanically fragile. Therefore, it isdesirable to use a substrate that is thick enough for safe mechanicalhandling.

The back contact DSCs are not transparent due to the use ofnon-transparent highly conducting materials. Consequently, these backcontact DSCs cannot be used for applications that require transparencysuch as building integrated photovoltaics (BIPV) or building appliedphotovoltaics (BAPV), where solar cells must both produce electricityand allow the passage of light to illuminate the inside of the building.

A known solution to making non-transparent solar cells transparentrelates to the introduction of pores and holes in the solar cell unit byremoving parts of the non-transparent cell material. Material can beremoved using e.g. laser technology or etching. The drawback of thisapproach is that the solar cell material is removed and wasted at theposition of the holes.

US 2013/255761 discloses a method for manufacturing a transparentworking electrode, whereby the working electrode includes a porous metalfoil. Pores are formed in the metal foil by needle penetration or laserablation. Also mentioned is a method of sintering titan powder andpressing titan fiber paper to create holes in the solar cell.

Some of the known solutions increase the complexity of the solar cell.These solar cells are more fragile and more prone to failure. Such solarcells are also more difficult to manufacture. Often, additional materialand process steps are needed using thin and delicate material.

There is a need for a solar cell, which is transparent, and has a goodor increased light to electric energy conversion efficiency and highconductivity. There is a need for a solar cell that can be applied to orintegrated in glass partitions of a structure, such as a building or avehicle. There is also a need for a solar cell that can be manufacturedat low cost. Suitably, no additional material or method steps should beneeded for manufacturing the transparent solar cells. There is a needfor a solar cell that can be manufactured without removing material fromthe solar cell, or without necessarily having to use laser or etchingtechniques and the like.

OBJECT AND SUMMARY OF THE INVENTION

The object of the present invention is to at least partially overcomethe above mentioned drawbacks.

This object is achieved by a dye-sensitized solar cell (DSC) accordingto the description herein.

The DSC comprises a porous isolating substrate, which has a first and asecond surface. A first porous layer comprising conductive particles isprinted on the first surface of the substrate to form a first conductivelayer. A second porous layer, comprising conductive particles, isprinted on the second surface of the substrate to form a secondconductive layer. The porous isolating substrate is thus positionedbetween the first and second porous layers. A third porous layer, theworking electrode, is printed on the first porous layer. This thirdporous layer is provided with light absorbing dye molecules. The DSCcomprises further a charge transfer medium for the transfer of chargesbetween the second porous layer (the counter electrode) and the thirdporous layer (the light absorbing layer). Preferably, the chargetransfer medium is transparent. This charge transfer medium may bepositioned in the pores of the porous layers and the porous isolatingsubstrate. All porous layers comprise a printed pattern, whereby eachporous layer has at least one non-transparent portion and at least onetransparent portion. The transparent portions of the porous layers andthe transparent portion of the porous isolating substrate are positionedrelative to each other so they form at least one continuous transparentpathway through the solar cell to allow light to penetrate through thesolar cell in a direction perpendicular to the first and secondsurfaces.

The non-transparent portions are non-transparent due to the fact thatthey include non-transparent material/particles. The non-transparentportions of the first and second porous layers include conductingparticles, for example metal particles, which are non-transparent. Thenon-transparent portions of the third porous layer include lightabsorbing dye molecules, which are non-transparent. However, due to thedegree of non-transparent particles in the non-transparent portion, thedegree of non-transparency may vary. With the term “non-transparentportion” is meant that at least 80% of incident light is prevented frompenetrating through the portion.

The transparent portions are transparent due to the fact that they donot include non-transparent material/particles or include only a fewnon-transparent particles. With the term “transparent portion” is meantthat it allows light transmission. However, there may be differentdegrees of transparency. For example, the transparent portions may betranslucent colored, such as translucent yellow, or opalescent.Preferably, the transparent portion should allow more than 50% lighttransmission, and preferably more than 70% light transmission.

The non-transparent portions of the first and second porous layers areelectrically conducting portions of the DSC. The transparent portions ofthe first, second and third porous layers and the substrate arenon-conducting portions of the DSC. The porous isolating substrate alsocomprises at least one transparent portion. The entire porous isolatingsubstrate can be transparent, or the substrate may not be transparentbut including one or more transparent portions, for example throughholes.

The transparent portions of the first, second and third porous layer andof the substrate are positioned so they form a continuous transparentpathway through the DSC, which allows light to pass through the DSC.Accordingly the DSC becomes transparent. Preferably, each of the porouslayers comprises a plurality of transparent portions, which togetherwith one or more transparent portions of the substrate form a pluralityof transparent pathway through the DSC.

The transparent portions, for example, in the form of holes or dots,allow light to pass through the DSC. The transparent portion(s) of thefirst and second porous layers can be positioned anywhere between thenon-transparent portion(s) as long as the non-transparent portion(s) ofthe layers form a continuous conducting pathway. This allows for thecreation of a large number of different printed patterns for a DSC, forexample as shown in FIGS. 4a -4 d.

When the transparent portions of all layers and the substrate arealigned or on top of each other in a direction perpendicular to thefirst and second surface, the transparent portions form one or morepathways within the DSC allowing light transmission through the DSC.However, light can be reflected within the structure and thereby passthrough the structure without the transparent portions overlap eachother.

By providing porous layers with printed patterns includingnon-transparent portion and transparent portions it is possible toachieve a transparent back contact DSC including non-transparent highlyconductive material. Each porous layer is printed as a patterncontaining one or more portions, for example in the form of dots, whereno conductive material is printed, such that light can penetrate throughthe transparent portions to achieve partial transparency of the DSC. Thetransparency level of the back contact DSC can then be adjusted byprinting transparent portions of varying sizes, varying shapes andvarying spacing. Additionally, advanced graphical patterns can beproduced by varying the size, shape and spacing of the transparentportions. Basic imaging techniques, such as the halftone technique, canfor example be used to design suitable print patterns resulting indesired graphical patterns. Consequently, by printing porous layersincluding transparent portions, it is possible to manufacture a backcontact DSC that is both transparent and has graphical design.

The present invention makes it possible to manufacture transparent backcontact DSCs for applications requiring transparency, such as inbuildings, where solar cells must both produce electricity and allow thepassage of light to illuminate the inside of the building.

A further advantage with using porous layers of printed patterns is thatno solar material has to be removed or wasted in an extra needed processstep (and no extra process step is needed). Consequently, by directlyprinting the back contact in the desired pattern it is possible toreduce the number of process steps and save solar cell material.Transparent conductors used in front contact solar cells have poorelectrical conductivity and suffer therefore a greater loss inconductivity when provided with transparent portions, and this factlimits the number of possible useful patterns, and it limits the maximumsize of such cells. In contrast, with the highly conducting DSC backcontact approach it is possible to achieve a larger number of usefulpatterns without compromising the cell size. It is also possible to adddifferent colors to the dots by coloring the front sheet or back sheetof the solar cell, thereby enhancing aesthetical quality.

The DSC can also be manufactured at low cost using relativeuncomplicated printing techniques. No holes need to be made in the DSC,i.e. no laser or etching techniques need to be applied to obtain thetransparent portions in the DSC. Thus, no additional materials ormanufacturing steps are needed to make the DSC according to thedescription herein.

The present invention makes it possible to produce a back contact DSChaving high electric conductivity, and thus allows for increased lightto electric energy conversion efficiency, while at the same time beingpartially transparent.

The DSC is made of thin layers, which together form a thin DSC. The DSCcan be easily installed in a glass partition of a structure, such as abuilding or vehicle. The pattern, i.e. the number and size of thetransparent portions, can be adjusted to the circumstances. For example,in countries having a warm climate, the number and/or size oftransparent portions can be limited to prevent sun from entering intothe structure, while in countries with less sunlight, the number and/orsize of the transparent portions can be increased to allow a maximumamount of light to enter the structure. Thus, the share of the area ofthe transparent portion(s) in the total area of the porous layers mayvary depending on the application of the solar cell. Preferably, thearea of the at least one transparent portion of each porous layer isbetween 10% and 70% of a total area of each porous layer, and typicallythe area of the at least one transparent portion of each porous layer isbetween 30% and 60% of a total area of each porous layer. Preferably,the area of the transparent portion(s) is similar in each porous layer.

In an embodiment, the at least one transparent portion of the porouslayers are arranged to at least partly overlap each other to ensure thatlight is allowed to penetrate through the porous layers.

In a further embodiment, the printed pattern of the third porous layercorresponds to the printed pattern of the first porous layer. In oneembodiment, the printed pattern of the second porous layer correspondsto the printed pattern of the first and third porous layers. It isconvenient to use the same pattern for all three porous layers. Further,the production of DSCs providing a graphical pattern when light ispenetrated through the DSC is facilitated.

The wording “corresponding pattern” when used in this specification istaken to specify “patterns having the same shape and the sameorientation”.

According to an embodiment of the invention, the solar cell comprises aplurality of connection elements, for example busbars, electricallyconnected to the first and second porous layers for connecting the firstand second porous layers to an external electric circuit, and theprinted patterns of the first and second porous layers are designed sothat the non-transparent portions are in direct electric contact with atleast one of the connection elements. This embodiment ensures that thecurrent generated by the light is transported to the external circuit,and accordingly ensures high efficiency of the electrical powerproduction of the DSC.

The third porous layer is a light absorbing layer, and its primaryfunction is to absorb light and convert the light into electricalenergy. The first and second porous layers are conductive layers. Theprimary function of the first porous layer is to collect current fromthe third porous layer and to transport the collected current to anexternal electric circuit. The primary function of the second porouslayer is to receive the current from the external electric circuit andto transport the current to the charge transfer medium. In order toefficiently collect and transport current to the external electriccircuit, all of the non-transparent portions of the first porous layershould be electrically connected to the connection element(s) of thefirst porous layer, to provide one or more continuous electricallyconducting paths between the non-transparent portions of the firstporous layer and the external electric circuit. In order to efficientlytransfer the current from the external electric circuit to the chargetransfer medium, all of the non-transparent portions of the secondporous layer should be electrically connected to the connectionelement(s) of the second porous layer, thereby providing one or morecontinuous electrically conducting paths between the non-transparentportions of the second porous layer and the external electric circuit.

In one embodiment, the printed pattern includes a plurality oftransparent portions distributed in one non-transparent portion. Thetransparent portions are, for example, transparent dots distributed in anon-transparent portion. The non-transparent portion forms a continuousconducting layer for transportation of current to and from the externalelectrical circuit. The transparent portions may be arranged to form agraphical pattern together with the non-transparent portion.

Preferably, the first and second layers are porous conductive powderlayers. This means that the layers were produced by deposing conductiveparticles in solid form. The solid particles are metal based and can bepure metals, metal alloys or metal hydrides or hydrides of metal alloysor mixtures thereof. The porosity of the porous conductive powder layerscan be between 15% and 85%. A porosity between 30% and 70%, or between40% and 60%, is preferred.

The transparent portion(s) of the porous isolating substrate can beachieved in different ways. Either, the entire substrate is transparentor only parts of the substrate are transparent.

In one embodiment, the charge transfer medium has a first refractionindex and the porous isolating substrate comprises material having asecond refraction index, whereby the difference between the first andsecond refraction index is less than 0.2. By having a charge transfermedium having a refraction index that is similar to the refraction indexof the substrate, the substrate becomes transparent, or at leastsemitransparent. The smaller the difference in refraction between thecharge transfer medium and the substrate, the higher the transparency ofthe substrate becomes. Thus, the difference between the refraction indexof the charge transfer medium and the refraction index of the substrateshould be as small as possible in order to achieve as high transparencyas possible of the substrate.

In another embodiment, the porous isolating substrate comprises atranslucent material, for example glass fibers or quartz fibers.

In another embodiment, the porous isolating substrate comprises one ormore transparent portions of a transparent plastic material.

In a further embodiment, said at least one transparent portion of theporous isolating substrate is a through hole extending between the firstand second surface of the porous isolating substrate.

The invention also relates to a use of the dye-sensitized solar cell, asdefined above, in a glass partition of a structure.

This object is also achieved by a method for manufacturing a transparentdye-sensitized solar cell, as defined herein.

The method comprises printing a first porous layer comprising conductingparticles on a first surface of an porous isolating substrate comprisingat least one transparent portion, printing a second porous layercomprising conducting particles on a second surface of the porousisolating substrate, printing a third porous layer on top of the firstporous layer, and dying the third porous layer with light absorbingmolecules, and each of the first, second and third porous layers areprinted in pattern including at least one non-transparent portion and atleast one transparent portion, and the patterns are printed such thatsaid transparent portions of the porous layers and said transparentportion of the porous isolating substrate form at least one continuoustransparent pathway through the solar cell, to allow light to penetratethrough the solar cell.

An advantage with this method is that no solar material has to beremoved or wasted and no extra process step is needed. Consequently, bydirectly printing the porous layers in the desired pattern it ispossible to reduce the number of process steps and save solar cellmaterial.

In one embodiment, the patterns are printed such that said transparentportions of the porous layers and said transparent portion of the porousisolating substrate at least partly overlap each other in a directiontransvers the first and second surface.

In one embodiment, the at least one non-transparent portion of the thirdporous layer is printed on top of the at least one non-transparentportion of the first porous layer. This means that the non-transparentportion(s) of the third porous layer is equal in size or smaller thanthe non-transparent portion(s) of the first porous layer.

In one embodiment, the patterns of the first, second and third porouslayers correspond to each other, i.e. the shape and size of thetransparent and non-transparent portions of porous layers are equal.This embodiment facilitates the production of the DSC.

In one embodiment, the printed pattern is printed using screen printing.Screen printing is a useful method to print the pattern. However, it isalso possible to use other printing methods.

In one embodiment, the method comprises punching the porous insolatingsubstrate to provide at least one through-hole extending between thefirst and second surface of the porous isolating substrate. Thesubstrate is provided with one or more through holes before printing thelayers. The through hole(s) form transparent portions extending throughthe substrate. This method is a simple way to provide transparentportions of the substrate.

In one embodiment of the method, the first and second porous layers areformed by printing a deposit comprising conductive particles onto thesubstrate, and sintering the conductive particles for forming conductinglayers.

In one embodiment of the method, a porous conductive powder layer isformed on one side of the porous isolating substrate and a second porousconductive powder layer is formed on the other side of the porousisolating substrate.

In another embodiment of the method, the deposit comprises a catalystfor forming a second porous conductive powder layer.

In a further embodiment of the method the third porous layer comprisesTiO₂ and the first and the second porous layer comprise titaniumparticles.

In a further embodiment the titanium particles are formed by heatdecomposition of printed titanium hydride particles.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained more closely by the description ofdifferent embodiments of the invention and with reference to theappended figures.

FIG. 1 shows schematically a dye-sensitized solar cell according to theprior art.

FIG. 2 shows schematically a cross-section of a dye-sensitized solarcell according to an embodiment of the invention.

FIG. 3 shows schematically a cross-section of a dye-sensitized solarcell according to another embodiment of the invention.

FIGS. 4a-d show examples of suitable designs for the printed pattern ofthe porous layers of a dye-sensitized solar cell according to theinvention.

FIGS. 5a-b show examples of embodiments for a DSC that could suitably beused.

FIG. 6 illustrates an example of a method for manufacturing adye-sensitized solar cell according to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 2 shows an example of a dye-sensitized solar cell (DSC) accordingto a first embodiment of the invention. The DSC comprises a porousisolating substrate 10 having a first surface 11 and a second surface12. In this embodiment, the porous isolating substrate 10 is transparentor becomes transparent when it is emerged in a charge transfer medium.For example, the substrate is made of a translucent material such asglass fibers or quartz fibers. The DSC further includes a first porouslayer 14 comprising conducting particles printed on the first surface 11of the porous isolating substrate to form a first conductive layer, anda second porous layer 16 comprising conducting particles printed on thesecond surface 12 of the porous isolating substrate to form a secondconductive layer. In the following the first porous layer is called thefirst conductive layer and the second porous layer is called the secondconductive layer. The porous isolating substrate 10 is disposed betweenthe first and second conductive layers 14, 16.

A third layer 18 including metal oxide particles and light absorbing dyemolecules is deposited on the first conductive layer 14. In thefollowing the third layer is called the light absorbing layer. The lightabsorbing layer 18 is printed on top of the first layer. The metal oxideparticles are then dyed with light absorbing dye molecules. The lightabsorbing layer 18 forms a working electrode. The first conductive layer14 is adapted to extract photo-generated electrons from the lightabsorbing layer. Preferably, the first, second and third layers areporous layers. The DSC further includes a transparent charge transfermedium for transferring charges between the layers. The charge transfermedium, such as an electrolyte, is infiltrated in the pores of the lightabsorbing layer, the conductive layers and the substrate. The chargetransfer medium forms a continuous medium between the layers, therebyenabling transport of electrical charge between the light absorbinglayer and the second conductive layer. The charge transfer medium iscomprised in the pores of the layers and substrate in order to transfercharges from the light absorbing layer to the second conductive layer.The charge transfer medium is, for example, a liquid electrolyte. Toimprove the transparency of the substrate, the charge transfer mediumcan be selected having a refraction index close to the refraction indexof the porous isolating substrate. Preferably, the difference betweenthe refraction indexes is less than 0.2. By having a charge transfermedium in the form of an electrolyte having a refraction index which issimilar to the refraction index of the substrate, the substrate becomestransparent, or at least semitransparent.

The first conductive layer 14 is used to collect electrons generated bythe light absorbing layer 18 and also to transport the electrons via anexternal electrical circuit (not shown) to the second conductive layer16. The second conductive layer 16 is used to transfer the electrons tothe charge transfer medium. The charge transfer medium transfers theelectrons back to the light absorbing layer thereby completing theelectrical circuit.

Each of the layers 14, 16, 18 comprise a printed pattern including atleast one transparent portion 20, 21, 22 and at least onenon-transparent portion 24, 25, 26. In this embodiment, each of thelayers includes a plurality of transparent portions. The transparentportions of the layers are positioned relative to each other so theyform continuous transparent pathways through the solar cell in adirection perpendicular to the first and second surface of thesubstrate. Suitably, the printed pattern is identical in the threelayers 14, 16, 18. Suitably, the printed patterns haves the sameposition and orientation in the different layers so that correspondingtransparent portions of the layers are aligned. However, it is possibleto have different patterns as long as the transparent portions of thelayers at least partly overlap each other. The non-transparent portionsof the first and second conductive layers are electrically conducting,and are arranged to form one or more conducting paths in a directionparallel to the first and second surfaces of the substrate in each ofthe first and second conductive layer. Preferably, the non-transparentportions of first and second conductive layers form at least onecontinuous current path in each layer.

The solar cell comprises at least one connection element 34 electricallyconnected to the first conductive layer for connecting the firstconductive layer to an external electric circuit (not shown), and atleast one connection elements 36 electrically connected to the secondconductive layer for connecting the second conductive layer to theexternal electric circuit. For example, the connection elements 34, 36are busbars. In one embodiment, the solar cell includes two connectionelements connected to the first conductive layer and disposed onopposite sides of the first conductive layer, and two connectionelements connected to the second conductive layer and disposed onopposite sides of the second conductive layer. The connection elementsmay extend along the entire side of the layers. Preferably, the printedpatterns of the first conductive layer is designed so that thenon-transparent portions 25 are in direct electric contact with theconnection element 34, and the printed patterns of the second conductivelayer is designed so that the non-transparent portions 26 of are indirect electric contact with the connection element 36.

In order to efficiently conduct away current from the light absorbinglayer, the non-transparent portions of the first conductive layer shouldprovide a direct electrically conducting path from the light absorbinglayer to the connection elements. Further, in order to efficientlytransfer current from the external electric circuit to the chargetransfer medium, the non-transparent portions of the second conductivelayer should provide a direct electrically conducting path to theconnection elements. Consequently the first and second conductive layersshould be printed in such a way that “islanding” of the non-transparentportions is avoided. Therefore the first and second conductive layersshould preferably be a continuous conductive layer disrupted bytransparent portions, where the positioning of the transparent portionsdoes not cause islanding or isolation of non-transparent portions.Furthermore, the printed pattern should be designed taking into accountthe conductivity of the back contact layer, the distance the currentmust travel, and the electrical current produced by the light absorbinglayer such that electrical losses is minimized in order to achievemaximum electrical power.

The DSC also includes a first sheet 28 covering a top side of the DSCand a second sheet 29 covering a bottom side of the DSC and acting asliquid barriers for the electrolyte. The first and second sheets 28,29needs to be transparent, allowing light to pass through. The sheets 28,29 are, for example, made of a transparent polymer material.

FIG. 3 shows an example of a dye-sensitized solar cell according to asecond embodiment of the invention. Like or corresponding parts in theFIGS. 2 and 3 are indicated with like numerals. The embodiment shown inFIG. 3 differs from the embodiment shown in FIG. 2 in that it includes aporous isolating substrate 30 made of a non-transparent material. Toallow light to pass through the substrate 30, the substrate is providedwith at least one transparent portion 32 extending between the first andsecond surface of the substrate. The transparent portions 32 are, forexample, through-holes or portions of a transparent plastic materialextending between the first and second surface. The transparent portions32 of the substrate are positioned relative the transparent portions 20,21, 22 of the layers such that they form a continuous pathway throughthe DSC for the light. Preferably the transparent portions 32 of thesubstrate and the transparent portions 20, 21, 22 of the layers arealigned, as shown in FIG. 3.

FIGS. 4a-d shows examples of different suitable designs for the printedpattern. The transparent portions are white and the non-transparentportions are black in the figures. The DSC may be printed in a patternof a logo or brand name. Also, one or more colours may be used in theDSC. Thus, the DSC can be used for commercial purposes in combinationwith harvesting energy from sun light. Preferably, the printed patternis designed so that the non-transparent portion(s) extend from one endof the layer to the other end of the layer to form at least onecontinuous conducting path from one end of the layer to the other end ofthe layer. This is particularly important for the first and secondconductive layers, which main function is to conduct current. Neithershould the positioning of the transparent portions cause “islanding” orisolation of the non-transparent portions.

FIG. 4a shows an example of a printed pattern including onenon-transparent portion and a plurality of transparent portionsdistributed in the non-transparent portion. The transparent portions areshaped as dots.

In another embodiment, the printed pattern includes a plurality ofnon-transparent portions and plurality of transparent portionsdistributed between the non-transparent portions. FIG. 4b shows apattern including a plurality of non-transparent portions in the form ofstrips extending from one end of the pattern to the other end of thepattern thereby forming a plurality of electrically conducting paths,and a plurality of transparent portions extending between thenon-transparent portions.

FIGS. 4c and 4d show other types of patterns having in common that thenon-transparent portions form at least one continuous conducting pathfrom one side of the pattern to the opposite side of the pattern.

FIGS. 5a-b show examples of other embodiments of the DSC. Differenttypes of dye-sensitized solar cells (DSCs), whereby the different layersof the cell can be printed on top of each other, can be used tomanufacture the DSC defined in claim 1. The present invention is notlimited to a specific embodiment of a DSC.

Another type of DSC is shown in FIG. 5a . The DSC differs from theembodiments of FIGS. 2 and 3 in that the solar cell includes a porousisolating layer 5 disposed between the first and second conductivelayers 2, 3 and a conductive layer 6 disposed between the porousisolating layer 5 and the second conductive layer 3. The conductivelayer 6 includes a porous substrate 4 made of an isolating material andconducting particles forming a conducting network through the isolatingmaterial. The additional isolating layer 5 is printed on the firstsurface of the substrate 4. The first conductive layer 2 is printed onthe additional isolating layer 5 and a second conductive layer 3 isprinted on the second surface of the substrate 4. A working electrode 1is printed on the first conductive layer 2. A charge transfer medium iscomprised in the layers and substrate in order to transfer chargesbetween second conductive layer 3 and the working electrode 1. Furtherdetails about this embodiment are disclosed in WO 2014/184379, which ishereby incorporated by reference. In order to achieve a transparent DCS,the working electrode 1 and the conductive layers 2, 3, are printed in apattern including transparent and non-transparent portions in the sameway as described with reference to FIGS. 2 and 3. Further, theconductive layer 6 including the substrate 4 can be provided withtransparent portions in the form of through holes extending through thelayer 6. The isolating layer 5 can be printed with the same pattern asthe first and second conductive layers, or be provided with throughholes in the same way as the conductive layer 6.

FIG. 5b shows an embodiment of a DSC comprising a plurality ofdye-sensitized solar cell units arranged adjacent to each other andconnected in series. The DCS comprises a working electrode 1, a firstconductive layer 2 for extracting photo-generated electrons from theworking electrode, a counter electrode including a second conductivelayer 3, and electrolyte for transferring electrons from the counterelectrode to the working electrode. The DSC further comprises a seriesconnecting element 8 for electrically connecting the counter electrodeto a working electrode of an adjacent cell unit. The DCS comprises aporous insulating substrate 4 having the first conductive layer 2printed on the first surface of the substrate 4 and the secondconductive layer 3 printed on the second surface. The working electrode1 is printed on the first conductive layer.

The series connecting element 8 is a conductive layer penetratingthrough the porous insulation substrate 4 and extending between thefirst conductive layer 2 of one of the cell units and the secondconductive layer 3 of the adjacent cell unit, thereby electricallyconnecting the first conductive layer of one of the cell units with thesecond conductive layer of the adjacent cell unit. Spaces 7 a and 7 b,between cell units a, b, c, are also shown. Further details about thisembodiment are disclosed in WO 2013/149787, which is hereby incorporatedby reference. In order to achieve a transparent DCS, the substrate 4 canbe provided with through holes positioned between the series connectingelements 8. The working electrode 1 and the conductive layers 2, 3, areprinted in patterns including transparent and non-transparent portionsin the same way as described with reference to FIGS. 2 and 3. However,the printed pattern of the first and second conductive layers shouldinclude non-transparent portions at least partly overlapping the seriesconnecting elements 8 to electrically connect the conductive layer withthe series connecting elements 8. Further, the spaces 7 a-7 b aretransparent portions of the layers.

In one embodiment, the porous isolating substrate 4 comprises a wovenfabric and non-woven fabric. Further details about this embodiment aredisclosed in WO 2013/149789, which is hereby incorporated by reference.Examples of other DSCs that can suitably be used in the presentinvention are for example disclosed in WO2012/045881, which is herebyincorporated by reference.

The porous isolating substrate can be made of a material that issuitable for printing. The substrate can be made of paper, such as papermade of micro fibres that may be a woven fabric and/or a non-wovenfabric. Preferably, the porous isolating substrate is a ceramicmicrofiber-based substrate, such as a glass microfiber or a ceramicmicrofiber substrate. Glass fibers, aluminosilicate fibers or quartzfibres may be used. The porosity of the porous isolating substrate willenable ionic transport through the substrate. The substrate comprises atleast one transparent portion. The substrate may comprise a plurality oftransparent portions. The transparent portion may be a through holeextending between the first and second surface, where the material ofthe substrate 4 has been removed. This through hole may filled withelectrolyte or a transparent material, such as a plastic.

The non-transparent portions of the light absorbing layer 18 includemetal oxide particles, for example TiO₂ particles, dyed with lightadsorbing dye molecules. The non-transparent portions of the conductivelayers 14, 16 comprise conductive metal particles. The material formingthe first and second conductive layer 2, 3 is suitably porous. The firstand second conductive layers 14, 16 can for example be made of amaterial selected from a group comprising titanium, titanium alloys,nickel, nickel containing alloys, chromium containing alloys, graphite,and amorphous carbon, or mixtures thereof. Suitably, the first andsecond conductive layers are made of titanium or a titanium alloy, ormixtures thereof.

Depending on the nature of the charge transfer medium, either ions orelectrons and holes can be transported between the second conductivelayer and the light absorbing layer. Examples of electrolytes are liquidelectrolytes (such as those based on the I—/I3-, redox couple or cobaltcomplexes as redox couple), gel electrolytes, dry polymer electrolytesand solid ceramic electrolytes. When electrolytes are used as chargetransfer medium, the counter electrode is normally equipped with acatalytic substance that serves the purpose of facilitating the transferof electrons to the electrolyte. Semiconductors can be used as chargetransfer medium to transport electrons and holes between the secondconducting layer and the light absorbing layer. Examples ofsemiconductors are inorganic semiconductors, such as CSCN or CuI, andorganic semiconductors, such as Spiro-OMeTAD. When semiconductors areused as charge transfer medium the counter electrode is normallyequipped with a substance that serves the purpose of creating a goodelectrical contact, i.e., a good ohmic contact, between the counterelectrode and the charge transfer medium.

The DSC according to the invention can suitably be used to provideenergy to structures, such as buildings or vehicles. The DSC can bepositioned in or on any partition of the structure. A partition can beany area of the structure, such as a wall or an opening between thewalls in which a window can be positioned. The DSC is especiallysuitable for use in an area of the structure where light enters thestructure, such as a glass partition of a building. Other examples maybe glass partitions in a vehicle, such as a car or a bus.

The area of the transparent portion(s) of the printed pattern can bebetween 10% and 80% of the total area of the layer. The amount of lightthat passes through the transparent DSC can be varied by varying thearea of transparency of the total area of the DSC. This allows for greatflexibility in the use of the DSC. For example, in a warm climate, itmay be desired to reduce the amount of sunlight passing through awindow, while at the same time energy is needed for air conditioning. Inthis case, a DSC can be designed having a printed pattern with only afew transparent portions and/or transparent portions of a small size. Ina colder climate on the other hand, it may be desired to let as muchsunlight enter the building as possible. For this situation a DSC can bedesigned having a printed pattern with a large amount of transparentportions and/or transparent portions of a large size.

Method

The DSC according to the invention can be manufactured in various ways.WO2013/053501 describes screen printing techniques that can be used forthe manufacturing of the DSC according to the present invention.WO2013/053501, especially page 4 to 7, is hereby incorporated byreference. Examples of printing techniques are slot die coating,gravure, screen printing, knife coating, blade coating, doctor blading,flexo printing, dip coating or spraying. The term printing also coversdry powder deposition. The dry powder deposition can be made by, forexample, sieving or electrostatic powder deposition.

Screen printing is a printing technique that uses a woven mesh tosupport an ink-blocking stencil to receive a desired image. The attachedstencil forms open areas of mesh that transfer ink or other printablematerials which can be pressed through the mesh as a sharp-edged imageonto a substrate. A fill blade or squeegee is moved across the screenstencil, forcing or pumping ink into the mesh openings for transfer bycapillary action during the squeegee stroke. Basically, it is theprocess of using a stencil to apply ink onto a substrate. Screenprinting is also a stencil method of print making, in which a design isimposed on a screen of polyester or other fine mesh, with blank areascoated with an impermeable substance. Ink is forced into the meshopenings by the fill blade or squeegee, and onto the printing surfaceduring the squeegee stroke. Screen printing is also known as silkscreen,serigraphy, and serigraph printing.

The method comprises printing a first layer on a first surface of anporous isolating substrate using ink comprising conductive particles,printing a second layer on a second surface of the porous isolatingsubstrate using ink comprising conductive particles, and printing athird layer on top of the first layer using ink comprising metal oxideparticles, dying the metal oxide with light absorbing molecules. Each ofthe layers are printed in pattern including at least one non-transparentportion and at least one transparent portion, and the patterns areprinted such that the transparent portions of the first, second andthird layers at least partly overlap each other.

One example of the method is described below with reference to FIG. 6.

In a first step one or more holes are formed into a porous isolatingsubstrate, for example a glass microfiber substrate.

In a second step a first conductive powder layer is produced by printinga pattern including transparent portions on one side of the substrate byscreen printing and using an ink including conductive particles. The inkmay be prepared from a mixture of TiH₂ with an organic solvent, such asterpineol. The printed pattern corresponds with the non-transparentportions of the substrate.

In a third step the deposited ink is dried.

In a fourth step, the substrate with the deposited conductive particlesis vacuum sintered to obtain a first porous conductive powder layer.

In a next step a second conductive powder layer is produced by printinga pattern including transparent portions on the other side of thesubstrate by screen printing using an ink including conductiveparticles. The printed pattern of the second conductive powder layercorresponds with the printed pattern of the first conductive powderlayer so that the transparent portions of the first and second layer arealigned. The deposited ink is dried and the deposited conductiveparticles are vacuum sintered to obtain a second porous conductivepowder layer.

In a next step, a TiO₂ based ink is deposited onto the first porousconductive powder layer using the same printing pattern and preparationsteps as described above for the first porous conductive powder layer.The printed pattern corresponds with the printed pattern of the firstand second conductive powder layer so that the transparent portions ofthe TiO₂ layer and first and second conductive powder layers arealigned. Optionally, two to three layers of TiO₂ based ink are printedin the same pattern onto the first layer of TiO₂ based ink prior tosintering this layer.

In a further step, dye molecules are applied to the TiO₂ layer to form aporous light absorbing layer.

The obtained DSC may then be filled with electrolyte and sealed.

Alternatively, the structure including a porous isolating substrate, afirst porous conductive powder layer and dye-sensitized TiO₂ layer canthen be sandwiched together with a second structure produced accordingto steps one to four, and having the same printing pattern.

In yet an alternative method the holes in the substrate are formed afterthe drying step, or after the sintering step.

EXAMPLES Example 1 Porous Conductive Powder Layer on a Ceramic Substrate

An ink was prepared by mixing TiH₂ with terpineol. The ink was then beadmilled for 25 minutes at 5000 RPM using 0.3 mm zirconia beads. Thezirconia beads were separated from the ink by filtration. A laser wasused to drill a circular through hole with a diameter of 5 mm in thecenter of a 4 cm×4 cm 45 micrometer thick glass microfiber basedsubstrate. The filtered ink was then printed on top of the glassmicrofiber based substrate using a printing pattern consisting of a 2cm×2 cm square with a circular hole in the center with a diameter of 6mm. The printing pattern was registered concentrically on top of thesubstrate such that the circular through hole and the circular printingpattern shared the same center. After printing, the deposited ink wasdried at 200° C. for 5 minutes. Subsequently, the coated glassmicrofiber substrate was vacuum sintered at 600° C. The pressure duringsintering was lower than 0.01 Pa (0.0001 mbar). The resulting porousconductive powder layer was a titanium metal porous film.

Subsequently, a TiO₂ based ink (or TiO₂-black) was printed onto theporous conductive powder layer using the same printing pattern andpreparation steps as was used for the TiH₂.

Prior to printing the substrate may be passed through heated rubbercoated rollers causing a smoothening of the surface of the substrate.The substrate may also be treated with colloidal silica before passingthe substrate through rubber coated rollers.

Alternative substrates are a substrate based on aluminosilicate fibres,or a mixture of aluminosilicate fiber and glass microfiber or quartzfibers

Example 2 Porous Conductive Powder Layer Printed on a Ceramic Substrate

An ink is prepared by mixing TiH₂ with terpineol. The ink was then beadmilled for 30 minutes at 4000 RPM using 0.3 mm zirconia beads. Thezirconia beads were separated from the ink by filtration. A hole punchwas used to punch a square through hole with an edge length of 5 mm inthe center of a 4 cm×4 cm 67 micrometer thick aluminosilicate microfiberbased substrate. The filtered ink was then printed on top of themicrofiber based substrate using a printing pattern consisting of a 2cm×2 cm square with a square hole in the center with an edge length of 6mm. The printing pattern was registered concentrically on top of thesubstrate such that the square through hole and the square printingpattern shared the same center and such that the edges of the twosquares were aligned.

After printing the ink was dried at 200° C. for 5 minutes. Subsequentlythe coated ceramic substrate was vacuum sintered at 850° C. for 30minutes and then cooled down to around 20° C. The pressure duringsintering was lower than 0.01 Pa (0.0001 mbar). The resulting porousconductive powder layer was a titanium metal porous film. Subsequently,a TiO₂ based ink (or TiO₂-black) was printed onto the porous conductivepowder layer using the same printing pattern and preparation steps aswas used for the TiH₂. The thickness of the porous conductive powderlayer was 16 micro-meter and the porosity 44%. The sheet resistancemeasured was less than 0.5 Ohm/sq.

Alternatively, the ceramic substrate is first printed with a porouslayer of TiO₂ to make the substrate surface smoother and more planarbefore printing the TiH₂ ink. We have found that the smoother thesubstrate surface before printing the TiH₂ ink the lower the porousconductive powder layer sheet resistance for a given porous conductivepowder layer thickness.

Example 3 Second Porous Conductive Powder Layer with Platinum Depositedon Ceramic Substrate

An ink is prepared by mixing TiH₂ with terpineol. The ink is bead milledfor 25 minutes at 5000 RPM using 0.3 mm zirconia beads. The zirconiabeads are separated from the ink by filtration. A laser was used todrill a circular through hole with a diameter of 5 mm in the center of a4 cm×4 cm 45 micrometer thick glass microfiber based substrate. Thefiltered ink was then mixed with hexachloroplatinic acid and printed ontop of the glass microfiber based substrate using a printing patternconsisting of a 2 cm×2 cm square with a circular hole in the center witha diameter of 6 mm. The printing pattern was registered concentricallyon top of the substrate such that the circular through hole and thecircular printing pattern shared the same center. The printed ink wasthen dried at 200° C. for 5 minutes. Subsequently, the printed ceramicsubstrate is vacuum sintered at 600° C. and then cooled down to roomtemperature. The pressure during sintering was lower than 0.01 Pa(0.0001 mbar). The resulting second porous conductive powder layercomprised a titanium metal porous film with catalytic amounts ofplatinum. Alternatively, the filtered ink is mixed with platinizedconducting particles prior to printing.

Alternatively, the filtered ink is not mixed with hexachloroplatinicacid. Instead a solution of hexachloroplatinic acid is printed onto thevacuum sintered porous conductive powder layer, which is then dried andheated to decompose the deposited hexachloroplatinic acid in order todeposit platinum on the surface thus forming a second porous conductivepowder layer.

The substrate may be based on aluminosilicate microfiber instead ofglass microfibers, or quartz fiber and glass microfiber.

The substrate may prior to printing be passed through heated rubbercoated rollers causing a smoothening of the surface of the substrate.

Example 4 Second Porous Conductive Powder Layer with Platinum Depositedon Ceramic Substrate

An ink was prepared by mixing TiH₂ with terpineol. The ink was then beadmilled for 25 minutes at 6000 RPM using 0.6 mm zirconia beads. Thezirconia beads were separated from the ink by filtration. A hole punchwas used to punch a square through hole with an edge length of 5 mm inthe center of a 4 cm×4 cm 67 micrometer thick aluminosilicate microfiberbased substrate. The filtered ink was then mixed with hexachloroplatinicacid and printed on top of the microfiber based substrate using aprinting pattern consisting of a 2 cm×2 cm square with a square hole inthe center with an edge length of 6 mm. The printing pattern wasregistered concentrically on top of the substrate such that the squarethrough hole and the square printing pattern shared the same center andsuch that the edges of the two squares were aligned. The printed ink wasthen dried at 200° C. for 5 minutes. Subsequently, the printed substratewas heat treated in vacuum and sintered at 850° C. for 30 minutes andthen cooled down to around 100° C. The pressure during sintering waslower than 0.01 Pa (0.0001 mbar). The resulting second porous conductivepowder layer comprises a titanium metal porous film with catalyticamounts of platinum. The thickness of the second porous conductivepowder layer was 20 micrometer and the porosity was 50%. The sheetresistance was lower than 0.6 Ohm/sq.

Alternatively, the filtered ink is not mixed with hexachloroplatinicacid. Instead a solution of hexachloroplatinic acid is printed onto thevacuum sintered porous conductive powder layer and then dried and heatedto decompose the deposited hexachloroplatinic acid in order to depositplatinum on the surface of the second porous conductive powder layer.The ceramic substrate may first be printed with a porous layer ofaluminosilicate to make the substrate surface smoother and more planarbefore printing the TiH₂ ink.

Example 5 Porous Conductive Powder Layers on Double Side Printed CeramicSubstrate

An ink was prepared by mixing TiH₂ with terpineol. The ink was then beadmilled for 25 minutes at 5000 RPM using 0.3 mm zirconia beads. Thezirconia beads were separated from the ink by filtration andhexachloroplatinic acid and ethyl cellulose was added to the filteredink. A laser was used to drill a circular through hole with a diameterof 5 mm in the center of a 4 cm×4 cm 45 micrometer thick glassmicrofiber based substrate. The ink was then printed on top of a glassmicrofiber based substrate using a printing pattern consisting of a 2cm×2 cm square with a circular hole in the center with a diameter of 6mm. The printing pattern was registered concentrically on top of thesubstrate such that the circular through hole and the circular printingpattern shared the same center. The printed ink was then dried at 200°C. for 5 minutes.

Another ink prepared by mixing TiH₂ with terpineol followed by beadmilling, filtration and ethyl cellulose addition was then printed ontothe opposite side of the glass microfiber substrate so that the firstprinted layer and the second printed layer are separated by the glassmicrofiber substrate. Additionally, the second printing pattern wasregistered concentrically on the second side of the substrate such thatthe circular through hole in the substrate and the circular printingpattern of the first print and the circular printing pattern of thesecond print shared the same center.

The double side printed substrate was then dried at 200° C. for 5minutes.

Subsequently, the double side coated ceramic substrate was vacuumsintered at 600° C. and then allowed to cool down to room temperature.The pressure during sintering was lower than 0.01 Pa (0.0001 mbar). Theresulting double sided printed substrate have a porous conductive powderlayer of titanium metal on one side and a second porous conductivepowder layer comprising titanium metal with catalytic amounts ofplatinum on the other side.

Alternatively, a circular through hole can be created by perform laserdrilling after the first and the second conductive layer has beenprinted and dried, respectively. By printing and drying continuous holefree conductive layers on each side of the substrate and then laserdrilling through all three layers there is no need to use a printingpattern with holes and there is no need to register the holes in theprinting pattern and therefore holes can be created by laser drillingthrough all three layers in one single step.

Alternatively, a circular through hole may be created by laser drillingthrough three layers in one single step after vacuum sintering of theprinted and dried first and second conductive layer, respectively.

Alternatively, a porous ceramic coating is deposited on the oppositeside of the ceramic substrate prior to laser drilling. Such a ceramicprint could be useful in order to prevent electrical contact between thefirst and second porous conductive powder layers.

The TiH₂ powder may be surface treated with platinum, e.g., by thermaldecomposition of a platinum salt deposited on the TiH₂ powder, beforemaking an ink.

Further, the filtered ink may be mixed with hexachloroplatinic acidinstead of mixing in platinized conducting particles.

Example 6 DSC Based on Porous Conductive Powder Layer Single SidePrinted on Ceramic Substrate

A 20 micrometer thick layer of TiO₂ ink containing 20 nm particles wasscreen printed onto the platinum free first porous conductive powderlayer side of a single side printed glass microfiber substrate producedaccording to example 1. The thickness of the dried TiO₂ ink layer was1-2 micrometer. A second 60 micrometer thick layer of TiO₂ ink wasprinted on top of the first layer of TiO₂ and dried. A third TiO₂ layerwas printed on top of the second TiO₂ layer and dried. Subsequently, theTiO₂ deposited structure was subjected to heat treatment in air at 500°C. for 20 minutes. After cooling down to around 70° C., the TiO₂deposited structure was immersed in a solution of 20 mM Z907 dye inmethoxy propanol and heat treated at 70° C. for 30 minutes andsubsequently rinsed in methoxy propanol and dried in dry air. Thestructure consisting of a glass microfiber substrate, porous conductivelayer and dye-sensitized TiO₂ was then sandwiched together with a secondstructure produced according to example 3. The second structureconsisted of a glass microfiber substrate with a titanium metal porousfilm containing catalytic amounts of platinum. The second structure wassandwiched with the first structure such that the titanium metal porousfilm containing catalytic amounts of platinum was brought in physicalcontact with the glass microfiber substrate side of the first structure.Thereby, the conductive layers of the first and second structures wereseparated electrically and physically by the glass microfiber substratein the first structure. Moreover, the circular hole in the secondstructure was registered concentrically, such that the through hole inthe substrate in the first structure and the printing pattern hole inthe first structure and the printing pattern hole in the secondstructure shared the same center. Thereafter, electrolyte was added tothe sandwich structure and the sandwich structure was sealed.

Example 7 DSC Based on Porous Conductive Powder Layer Double SidePrinted onto Ceramic Substrate

A 20 micrometer thick layer of TiO₂ ink containing 20 nm particles wasscreen printed onto the platinum free first porous conductive powderlayer side of a double side printed glass microfiber substrate producedaccording to example 5 or 6. The thickness of the dried TiO₂ ink layerwas 1-2 micrometer. A second 60 micrometer thick layer of TiO₂ ink wasprinted on top of the first layer of TiO₂ and dried. A third TiO₂ layerwas printed on top of the second TiO₂ layer and dried. Subsequently, theTiO₂ deposited structure was subjected to heat treatment in air at 500°C. for 20 minutes. After cooling down to around 70° C., the TiO₂deposited structure was immersed in a solution of 20 mM Z907 dye inmethoxy propanol and heat treated at 70° C. for 30 minutes andsubsequently rinsed in methoxy propanol. Thereafter, electrolyte wasadded to the porous conductive powder layer double side printed ceramicsubstrate and the structure was sealed.

Example 8 DSC Based on Porous Conductive Powder Layer Double SidePrinted onto Ceramic Substrate with Blocking Layer

An ink was prepared by mixing TiH₂ with terpineol. The ink was then beadmilled for 40 minutes at 5000 RPM using 0.3 mm zirconia beads. Thezirconia beads were separated from the ink by filtration andhexachloroplatinic acid and ethyl cellulose was added to the filteredink. A laser was used to drill a circular through hole with a diameterof 5 mm in the center of a 4 cm×4 cm 45 micrometer thick glassmicrofiber based substrate. The ink was then printed on the secondsurface of a glass microfiber based substrate equipped with a blockinglayer of nanocellulose, which was deposited on the first surface of thesubstrate. The printing pattern consisted of a 2 cm×2 cm square with acircular hole in the center with a diameter of 6 mm. The printingpattern was registered concentrically on top of the substrate such thatthe circular through hole and the circular printing pattern shared thesame center. The conducting particles in the ink were smaller than thepores of the substrate therefore the conducting particles penetrate thesubstrate and was printed into the substrate. The printed ink was thendried at 200° C. for 5 minutes.

Another ink prepared by mixing TiH₂ with terpineol followed by beadmilling, filtration and ethyl cellulose addition was then printed ontothe opposite side of the glass microfiber substrate so that the firstprinted layer and the second printed layer are separated by the glassmicrofiber substrate. Additionally, the second printing pattern wasregistered concentrically on the second side of the substrate such thatthe circular through hole in the substrate and the circular printingpattern of the first print and the circular printing pattern of thesecond print shared the same center. Additionally the second printedlayer was deposited onto the nanocellulose based blocking layer.

The double side printed substrate was then dried at 200° C. for 5minutes.

Subsequently, the double side coated ceramic substrate was vacuumsintered at 600° C. and then allowed to cool down to room temperature.The pressure during sintering was lower than 0.01 Pa (0.0001 mbar). Theresulting double sided printed substrate have a porous conductive powderlayer of titanium metal on one side and a second porous conductivepowder layer comprising titanium metal with catalytic amounts ofplatinum on the other side.

Subsequently, a 20 micrometer thick layer of TiO₂ ink containing 20 nmTiO₂ particles was screen printed onto the platinum free first porousconductive powder layer side of the double side printed glass microfibersubstrate. The thickness of the dried TiO₂ ink layer was 1-2 micrometer.A second 60 micrometer thick layer of TiO₂ ink was printed on top of thefirst layer of TiO₂ and dried. A third TiO₂ layer was printed on top ofthe second TiO₂ layer and dried. Subsequently, the TiO₂ depositedstructure was subjected to heat treatment in air at 500° C. for 20minutes. After cooling down to around 70° C., the TiO₂ depositedstructure was immersed in a solution of 20 mM Z907 dye in methoxypropanol and heat treated at 70° C. for 30 minutes and subsequentlyrinsed in methoxy propanol. Thereafter, electrolyte was added to theporous conductive powder layer double side printed ceramic substrate andthe structure was sealed.

1. A dye-sensitized solar cell comprising: a porous isolating substrate(10; 30) having a first surface and a second surface, a first porouslayer (14) comprising conducting particles printed on the first surfaceof the porous isolating substrate to form a conductive layer, a secondporous layer (16) comprising conducting particles printed on the secondsurface of the porous isolating substrate to form a conductive layer,whereby the porous isolating substrate (4; 10; 30) is disposed betweenthe first and second layers, a third porous layer (18) comprising lightabsorbing dye molecules deposited on the first layer, and a chargetransfer medium for transferring charges between the third and secondlayers, wherein each of the first and second porous layers comprise aprinted pattern including at least one non-transparent portion (24, 25,26) and at least one transparent portion (20, 21, 22) and the porousisolating substrate comprises at least one transparent portion (32),whereby said transparent portions of the porous layers and saidtransparent portion of the porous isolating substrate are positionedrelative to each other so they form at least one continuous transparentpathway through the solar cell.
 2. A dye-sensitized solar cell accordingto claim 1, wherein the at least one transparent portions (20, 21, 22)of the porous layers are arranged to at least partly overlap each other.3. A dye-sensitized solar cell according to claim 1, wherein the printedpattern of the third porous layer (18) corresponds to the printedpattern of the first porous layer (14).
 4. A dye-sensitized solar cellaccording to claim 3, wherein the printed pattern of the second porouslayer (16) corresponds to the printed pattern of the first and thirdporous layers (14, 18).
 5. A dye-sensitized solar cell according toclaim 1, wherein the solar cell comprises a plurality of connectionelements (34, 36) electrically connected to the first and second porouslayers (14, 16) for connecting the first and second porous layers to anexternal electric circuit, and the printed patterns of the first andsecond porous layers are designed so that the non-transparent portions(25, 26) are in direct electric contact with at least one of theconnection elements.
 6. A dye-sensitized solar cell according to claim1, wherein said printed pattern includes a plurality of transparentportions (20, 21, 22) distributed in the at least one non-transparentportion (24, 25, 26).
 7. A dye-sensitized solar cell according to claim1, wherein said at least one transparent portion (32) of the porousisolating substrate (30) is a through hole extending between the firstand second surface of the porous isolating substrate.
 8. Adye-sensitized solar cell according to claim 1, wherein an area of theat least one transparent portion of each porous layer (14, 16, 18) isbetween 10% and 70% of a total area of each porous layer, and preferablybetween 30% and 60% of a total area of each porous layer.
 9. Adye-sensitized solar cell according to claim 1, wherein said first andsecond porous layers are porous conductive powder layers.
 10. (canceled)11. A method for manufacturing a transparent dye-sensitized solar cell,wherein the method comprises: printing a first porous layer (14)comprising conducting particles on a first surface of an porousisolating substrate (10; 30), printing a second porous layer (16)comprising conducting particles on a second surface of the porousisolating substrate, printing a third porous layer (18) on top of thefirst porous layer, and dying the third porous layer with lightabsorbing molecules, wherein the porous isolating substrate comprises atleast one transparent portion (32), and each of the porous layers areprinted in patterns including at least one non-transparent portion (24,25, 26) and at least one transparent portion (20, 21, 22), and thepatterns are printed such that said transparent portions of the porouslayers and said transparent portion of the porous isolating substrateform at least one continuous transparent pathway through the solar cell.12. The method according to claim 11, wherein the patterns are printedsuch that said transparent portions of the porous layers and saidtransparent portion of the porous isolating substrate at least partlyoverlap each other in a direction transvers the first and secondsurface.
 13. The method according to claim 11, wherein the at least onenon-transparent portion of the third porous layer (24) is printed on topof the at least one non-transparent portion (25) of the first porouslayer.
 14. The method according to claim 11, wherein the patterns of thefirst, second and third porous layers (14, 16, 18) correspond to eachother.
 15. The method according to claim 11, wherein said printedpattern is printed using screen printing.
 16. The method according toclaim 11, wherein the method comprises punching the porous isolatingsubstrate to provide at least one through hole (32) extending betweenthe first and second surface of the porous isolating substrate (30).